1. Field of the Invention
This invention relates to a new process for recovering shale oil from raw oil shale. More particularly, the invention relates to a new process for treating raw oil shale to recover shale oil in high yield, improved quality and at a lower cost than possible with prior known techniques.
Specifically, the invention provides a new and improved process for recovering shale oil from raw oil shale in high yield and improved quality with greatly improved economics using a special integrated hydropyrolysis/thermal pyrolysis technique which has unusually low heat and energy requirements. The new process broadly comprises a continuous operation wherein the raw oil shale is crushed, ground and combined with hot recycle heavy oil to form a fluid slurry, the hot slurry is treated with hydrogen under elevated temperature and pressure for a short period. The slurry mixture then passes to a stripper operated at reduced pressure where the desired liquid products are stripped out for recovery and the remaining slurry is taken to a thermal retort where under fluidized bed conditions it is subjected to a temperature range by adding spent shale that has been burned in an air lift combustor at two different zones, the upper zone being operated such that the temperature is sufficient to vaporize the remaining slurry oil, and the lower zone being operated such that the temperature is sufficient to thermally retort spent shale from the hydropyrolysis chamber and thermally crack excess heavy gas oil, the resulting product being taken to a quench tower where the low molecular weight liquid product is recycled to the hydropyrolysis reactor for hydrogenation and heavy oil is recycled to the slurry mixer.
2. Prior Art
World wide demand for hydrocarbons and related products is continuing at a high annual rate. Crude petroleum and natural gas are basic in satisfying these demands but shortages can be forseen in the near future even though new oil and gas resources are being discovered. Therefore, alternate sources and feed stocks, such as coal, tar sands, oil shale and solid crudes are receiving greater consideration.
Oil shales found in large quantities in various locations throughout the world are an ideal source for obtaining additional quantities of hydrocarbons and related products. Oil shale consists of compacted sedimentary inorganic rock particles, generally laminated and partly or entirely encased with a high molecular weight organic solid material called kerogen, which is generally present in the amounts of about 6 to 30 percent by weight of the shale. Kerogen is derived from aquatic organisms or waxy spores and pollen grains, comprising hydrocarbons and complex organic-nitrogen, oxygen and sulfur compounds. Nitrogen in kerogen is largely present in the form of thiophene-type compounds. Crude shale oil produced from the oil shale by pyrolysis of the kerogen differs from crude petroleum by being more unsaturated and having a higher content of nitrogen compounds. Further, poor color stability and disagreeable odor of the shale products are related to the presence of these compounds.
Prior known methods for recovering oil from raw shale used principally a thermal means and more recently the use of molecular hydrogen. These methods have not been entirely satisfactory as they have generally resulted in a low conversion to the desired higher molecular weight liquid products and higher conversion of the kerogen to carbon and gas products which are of low economic value. Furthermore, the desired liquid products have been of low quality in that they have a high molecular weight and contain considerable amounts of the above-described nitrogen, sulfur, and oxygen contaminants. Finally, many of the prior known processes have required the use of considerable amounts of energy and elaborate equipment and are thus very expensive to operate.
Prior known processes for recovering oil shale which have one or more of the above-noted deficiencies include: Hoekstra--U.S. Pat. No. 4,414,433, Vasalos--U.S. Pat. No. 4,404,083, Bertelsen--U.S. Pat. No. 4,366,046, Sieg--U.S. Pat. No. 4,293,401, Tarman--U.S. Pat. No. 4,431,509, Hall--U.S. Pat. No. 4,421,603 and Schlinger--U.S. Pat. No. 3,617,470.
It is an object of the invention, therefore, to provide a new and efficient process for recovering shale oil from raw oil shale. It is a further object to provide a new process for recovering oil from raw oil shale which permits recovery of liquid hydrocarbon products in higher yields than possible heretofore. It is a further object to provide a process for recovering oil from raw oil shale of greatly improved quality. It is a further object to provide a process for recovering oil from raw oil shale which has significantly reduced quantities of nitrogen, oxygen and sulfur contaminants. It is a further object to provide a process for recovering shale oil from raw oil shale which process has unusually low heat and energy requirements. It is a further object to provide a process for recovering oil from oil shale which yields sufficient gas or liquid product to use in manufacturing its own hydrogen requirements. It is a further object to provide a process for recovering oil shale which uses equipment compatible with known processes and thus capable of being combined therewith. These and other objects of the invention will be apparent from the following detailed description thereof.